Light emitting diodes (LEDs) have been available since the early 1960s in various forms, and are now widely applied in a variety of ways, including signs and message boards, vehicle lights, and even interior lights. The relatively high efficiency of LEDs is the primary reason for their popularity. Tremendous power savings are possible when LEDs are used to replace traditional incandescent lamps of similar luminous output.
One aspect of high powered LED technology that has not been satisfactorily resolved is the removal of heat generated by the LED. LED lamps exhibit a substantial light output sensitivity to temperature, and in fact are permanently degraded by excessive temperature. Recently, very high performance LEDs have been commercialized. However, these LEDs emit a substantial amount of heat during their operation, which can permanently degrade the LED over time, resulting in a lower output and operating life. In ideal conditions, the life of the LED is 50,000-100,000 hours, however, this life can be shortened to less than 10% of the designed life due to the heat generated by these new super bright LEDs. Until recently, the higher light output was the trade-off for the shortened life due to the heat it generated.
To maximize the life of LEDs a heat sink coupled to the LEDs has been increasingly used. For example, aluminum or metal core printed circuit boards (PCB) have been used. These PCBs have a dielectric layer on top of the metal surface which acts as an electrical insulator between the circuitry and the metal base. The circuit traces are then formed on top of the dielectric, and the electronic components attached thereto. There are several ways to manufacture a metal core PCB. For example, thin FR4 or fiberglass circuit board that already has the circuitry printed onto it is mounted onto a metal substrate. Another method is to print the circuitry onto the dielectric material after it has already been mounted onto the metal substrate.
Due to the rise in popularity of LEDs, they are now widely used in architectural lamps and are becoming the standard in energy saving lighting applications. There are currently 500 million recessed lamps in America today and most of them have to be replaced with more efficient and eco-friendly lamps within few years. Light fixture designers and engineers are always challenged by the fact that a massive heat-sink is required to remove the heat from the LED, which is crucial to the life and the performance of the LED.
Currently designers use a die-cast aluminum alloy conical shape body/housing as the heat-sink. The LEDs are assembled on a metal core PCB and then mounted on the heat-sink with thermal conductive paste. The LED driver is then placed in a plastic housing which also houses the lamp socket and the whole assembly is attached to the aluminum alloy heat-sink.
However, there are several key problems with these designs. The first problem is that the aluminum alloys generally used to die cast these parts have silicone mixture in them for flow characteristics and smooth finish. Silicone causes the die cast alloy mixture to have a very low thermal conductivity ranging from 96.2 to 121 W/m-K. The thermal conductivity of non die cast aluminum alloy, which don't contain silicone in the mixture, such as extruded or rolled aluminum alloy is much higher, 167 W/m-K. This is 57% higher thermal conductivity which means that these aluminum alloys would dissipate the heat more than twice as fast compared to a die cast aluminum alloy. The second problem is that die-cast parts are expensive and consume way too much energy to produce them. They also break easily because of the silicone mixture. Another problem associated with the current designs is that the metal core PCB which has an aluminum core and it is covered with either a ceramic or polymer material as the dielectric. The dielectric material acts as a barrier for the heat to dissipate from the LEDs. Although many methods are used to make the heat dissipation better, but the fact remains that it is still an existing problem.
Another problem exists in the life expectancy between the LEDs themselves and the components used to operate them. A typical light socket is running on alternating current (AC) power, whereas an LED requires direct current (DC). An AC to DC converter (or also called a driver) is used to convert the AC power to DC power. The LED driver is inside the lamp assembly. The drivers must have an isolated transformer inside the driver unit to isolate the AC from DC to protect the consumers from getting electrical shocks. These drivers also have capacitors and other electronic components that have relatively shorter life than the LEDs. The drivers have a 5 year life in general, whereas the LED cluster would last more than 100,000 hours or over 12 years. Also, the LED cluster is usually the most expensive part of the lamp. So when the driver fails, the whole lamp must be discarded.
In summary the recessed lamps today that use die-cast heat-sink are expensive, have poor thermal conductivity, are heavy, require expensive tooling and use metal core PCBs that act as thermal barriers which slows heat dissipation. Also, when the LED driver fails, the whole light along with a functioning LED cluster must be discarded. Accordingly, there is a need for a LED light bulb with integrated heat sink and also a separable LED driver and cluster assembly that overcomes these drawbacks. The present invention fulfills these needs and provides other related advantages.